Tubular articles, in the form of woven, braided and knitted sleeving products have been made typically from a variety of plastics materials and mineral materials, such a glass fiber, as is well known in the art. Such products are in widespread use, for example, in the automotive and aerospace industries for bundling and protecting members such as wires, cables and tubing, for the reduction of noise and for protection of hoses and various other members from abrasion or from the deleterious effects of heat in high temperature environments.
It is a recognized problem with sleeving products or sleeves of this sort that, for some applications, installation thereof over elongated substrate members can be labor intensive. This is because of the requirement that the sleeve fit relatively snugly over the members to be protected in order to reduce vibration-induced noises and to maximise the protection afforded. As a consequence, a braided sleeve construction is preferred in which a first set of yarns extending helically in one rotational direction about a longitudinal axis is interbraided with a second set of yarns extending helically in the opposite rotational direction about said axis. Such braided sleeving can be axially compressed to reduce the helix pitch and thus correspondingly radially expanded for relatively easy advancement over the members to be protected, thereafter being stretched out axially, that is, extended, to increase the helix pitch and cause radial contraction onto the members.
However, it is sometimes difficult for the installer to maintain the tubular sleeve in the axially-compressed and radially expanded state while at the same time feeding it onto the members to be protected. As a consequence, there is a need for product improvements which facilitate installation of tubular articles such as sleeving products, particularly where access to the members to be covered is limited.
In this specification, to avoid misunderstanding of the complementary expansion and contraction which occurs in the longitudinal and radial directions, increase in the radial direction is referred to as "expansion" whereas increase in the longitudinal direction is referred to as "extension".
It is an object of the present invention to provide a braided tubular article, such as a sleeve, of simple and cost effective construction which mitigates the difficulties hitherto experienced in placing such tubular articles on, and contracting onto, elongate members.
In accordance with the present invention a braided tubular article comprises a plurality of yarns extending helically with respect to a longitudinal axis and interbraided with respect to each other into a tubular form of small helix pitch capable of significant axial extension and axial contraction by relative movement between the yarns, and is characterized by a plurality of restraining elements extending axially of the tubular form and coupled to the braided yarns to inhibit, by said coupling, axial extension of the tubular article in response to an axial force applied to the tubular form, and to permit axial extension of the tubular article in response to a said axial extension force in excess of a predetermined threshold level.
Thus, a braided tubular article according to the invention is braided in the radially-expanded, backed-up state and maintained in that state by the coupling between the restraining elements and braided yarns. This facilitates installation over elongate wires or other members such as hoses or cables. Once the article is threaded over the members and the braided tubular form is pulled axially with a force above the threshold to overcome the coupling between restraining elements and braid yarns, it extends axially and the tubular wall thereof contracts radially and possibly, but not essentially, into contact with members to be protected. After the article is axially extended it will stay in the radially contracted state due to frictional effects between the braided yarns.
The restraining elements may take any elongate form suitable for the function but preferably comprise warp elements braided with said tubular form. More preferably the warp elements are coupled to the braided yarns of the tubular body to inhibit said axial extension by frictional engagement between them. Each restraining element preferably is substantially inelastic lengthwise thereof. Such frictional effects, overcome during axial extension, exist following such extension and may, particularly in combination with such inelastic elements, have effect also in subsequently inhibiting axial contraction of the extended article.
Notwithstanding the form of the restraining elements, such coupling may comprise, or be supplemented by, a disruptable adhesive bond. Insofar as it is known to treat a braided tubular article by impregnating or coating with an anti-fraying agent to prevent fraying of cut ends and unraveling of the braided structure, the tubular article of the present invention may likewise be treated for the same purpose and also to effect a disruptable bond between the restraining elements and braid yarns. A water based agent is preferred, and more preferably a water based acrylic composition, such as a very dilute acrylic latex, although other agents may be used.
Restraining elements formed as warp elements in accordance with the preceding paragraphs are naturally essentially floating with respect to the braided tubular forms in that when the tubular article is extended beyond its initial manufactured length the restraining elements, being of lesser length than the extended article, end up at indeterminate axial positions. If it is desired to determine the final position of each restraining element, it may be coupled at a single predetermined attachment point thereof to the braided tubular form in a permanent attachment therewith.
Where each restraining element comprises a warp element braided with the yarns into the tubular article, it may comprise the same material as the interbraided yarns. It may comprise an individual monofilament or bundle of monofilaments. The monofilaments of such a bundle, which may comprise up to about three such monofilaments, may be twisted together or may be untwisted.
The warp elements (and interbraided yarns) may be made from a wide variety of materials, particularly those known because of their properties and stability as engineering thermoplastics, for example, being selected from the materials comprising nylon, peek and polyester.
For certain applications the warp elements may comprise multi-filament elements and/or braided or knitted warp beads, for example, multi-filament mineral fiber yarns.
Although any number of restraining elements may be employed, they are preferably disposed equidistantly spaced with respect to each other about the circumference of the tubular article. Conveniently, restraining elements in the form of the aforementioned warp elements are provided in pairs, the elements of each pair being diametrically opposed. With one pair of diametrically opposed warp elements the tubular article can, in addition to retaining the axially extended dimension, assume and retain a bent shape in a plane containing the warp elements, while having flexibility in respect of bending out of said plane. With two pairs of diametrically opposed warp elements the tubular article can retain its shape in three dimensions, that is, the axially extended dimension and in (wholly or in combination) the orthogonal planes containing the warp elements.